The ρ parameter and the CDF-II W-mass anomaly: observations on the role of scalar triplets

Abstract

Abstract The ρ parameter, together with the W and Z masses, acts as Occam’s razor on extensions of the electroweak symmetry-breaking sectors. We apply this to non-doublet Higgs scenarios, by examining the CDF-II claim on the W-boson mass. Suspending any judgment on the CDF claim, we show that in general, if one works at the tree level, theoretical models that predict ρ = 1 at the tree level are inconsistent with the CDF claims at 4–6 standard deviations if one confines oneself to the existing Z-boson mass and the earlier W-boson mass from either the global fit or the ATLAS data. We take some well-motivated scenarios containing one or more scalar SU(2) triplets in addition to the usual doublet and show that both a scenario including a complex scalar triplet and one with a complex as well as a real triplet (the Georgi–Machacek model) can be made consistent with the new data, where a small splitting between the complex and real triplet vacuum expectation values are required in the second scenario. We explore the consequences of this splitting, either at the tree level or via incalculable new physics contribution to W-boson mass and indicate as illustrations its implications in H ± W ∓ Z type interaction vertices.